In low-voltage circuit-breakers, known magnet arrangements are used in a pre-chamber, arranged between a breakpoint and an arc-extinguishing chamber, as a means of improving the running characteristics of the switching arc associated with the interruption of a short-circuit current or overcurrent. The effective magnetic induction applied to the switching arc can be dictated by the geometry, the polarity, the constituent magnetic material and the magnetization of the permanent magnet in an open magnetic circuit.
A magnetic arrangement of the above-mentioned type is described in EP 1 998 350 B1. This magnet arrangement includes two iron plates, which are laterally adjacent to a pre-chamber in a low-voltage circuit-breaker, and a permanent magnet for the delivery of the magnetic flux to the two iron plates. The resulting open-circuit magnetic induction in the pre-chamber between the two iron plates is used to improve the running characteristics of a switching arc which is generated when a direct current is interrupted.
An arc-extinguishing installation for a low-voltage circuit-breaker with a double break function is also known from EP 1 548 773 B1, in which the running characteristics of two switching arcs which are generated when an alternating current is interrupted, and which pass through one of two pre-chambers respectively during the interruption process, are improved by means of two casings of a magnetic material, one of which is associated with each of the two pre-chambers respectively. Each casing is provided with a U-section sheet, surrounds its associated pre-chamber in the lateral direction and is adjacent to one of the electric arc running rails for the direction of the lower root point of the switching arc.